1. Field of Invention
This invention relates to polymer films. More particularly, this invention relates to ultrathin polyarylate polymer films and their production.
2. Prior Art
In U.S. Pat. No. 2,760,233, a process is disclosed for preparing curved polymer sheets from polyesters. However, no specific solvent mixtures or ratios suitable for casting ultrathin, pinhole-free, polyarylate films are disclosed nor are any film thicknesses provided.
U.S. Pat. No. 3,551,244 discloses a process for preparing on a water surface films having thicknesses between 0.05 and 5.0 microns (i.e. between 500 and 50,000 angstroms). The patent discloses certain halogenated solvents, such as chloroform and chlorobenzene, as being suitable casting solvents and states that polyester films can be prepared. However, no specific solvent mixtures and ratios suitable for casting pinhole-free, polyarylate films with thicknesses less than 400 angstroms are disclosed.
In U.S. Pat. No. 3,933,561, a process for preparing polymer films having thicknesses less than 2.5 microns (eg. 1000 angstroms) is disclosed. Polyesters are listed as suitable polymers for use in the patent's process. However, polyarylates are not specifically disclosed nor are suitable solvent ratios for casting ultrathin, polyarylate films described.
U.S. Pat. No. 3,767,737 discloses a method for producing polymer membranes having thicknesses between 0.005 and 0.05 mils on a support liquid. Any polymer or copolymer capable of film casting is alleged by the inventor to be suitable for use in the process. However, polyarylate films are not disclosed nor are specific mixtures of solvents and appropriate solvent ratios for preparing void-free, polyarylate films having thicknesses of 400 angstroms or less.
U.S. Pat. Nos. 4,155,793, 4,279,855 and 4,374,891 disclose processes for preparing substantially void-free, ultrathin, permeable, polymeric membranes having thicknesses of 500 angstroms or less. Natural and synthetic polymers are asserted to be suitable for use in the disclosed process. However, only films prepared from organopolysiloxane-polycarbonate interpolymers mixed with polyphenylene oxide are disclosed in the examples. Polyarylate films are not disclosed nor are suitable solvent mixtures and ratios for casting polyarylate films having thicknesses of 400 angstroms or less.
Other patents, such as U.S. Pat. Nos. 2,631,334, 2,689,187 and 4,393,113, also disclose ultrathin polymeric films. However, polyarylate films are not disclosed in these patents.
In the prior art, the preparation of ultrathin, void-free, polyarylate, free-standing films with thicknesses of less than 400 angstroms generally has not been disclosed. Usually, when attempts are made to cast polymer films with thicknesses of less than 400 angstroms, defective films containing voids and other macroscopic defects usually result.
Therefore, it is an object of this invention to prepare ultrathin, polyarylate polymer films.
It is a further object of this invention to prepare pinhole-free, polyarylate polymeric films.
It is also an object of this invention to prepare free-standing, polyarylate films having thicknesses of 400 angstroms or less.
These and other objects are obtained by the products and process of the present invention.